NetBIOS is a network transport originally developed by IBM for small networks. It, and an extension of it called NetBEUI, are the transport layer used by the Client for Microsoft Networking. These two transports cannot deliver packets over a router because they rely on broadcast messages, which are not forwarded by routers.
NetBIOS over TCP/IP, solves that problem by encapsulating the NetBIOS or NetBEUI packets in IP packets. It converts between IP addresses and NetBIOS names, so that both TCP/IP and NetBIOS applications get the information in the expected format. Because IP packets can be forwarded by routers, you can use the NetBIOS applications over a router.
If you want to use NetBIOS applications (for example, the Windows ClipBook), you should enable NetBIOS over TCP/IP.
When you use NetBIOS over TCP/IP, you must tell Cisco TCP/IP Suite how to attempt to resolve NetBIOS names to IP addresses. You can use broadcast messages, WINS servers, a LAN Manager hosts file (LM Hosts), DNS servers, or any combination of these. What you use depends on what your network administrator has configured for your network.
For more information, see RFCs 1001 and 1002. RFC 1001 is a general overview.
There are several ways in which a NetBIOS name can be resolved to an IP address. The method you use depends on the facilities your network administrator has created for you. You might be required to create some of these resources yourself.
The first place NetBIOS looks to resolve a name to an IP address is the NBT cache on your workstation. This cache contains information about recently used NetBIOS names, and any entries from the LM host table that you preloaded into the NBT cache. You determine the entries that are preloaded when you create or modify LM host table entries from the LM Host Table tab in the Cisco TCP/IP Suite Configuration Utility. (The NBT cache is automatically created and maintained for you.)
If NetBIOS cannot find the name in the NBT cache, it either issues a broadcast message to the network, asking for the machine that uses the name to respond with its IP address, or it looks in the WINS servers that you have identified on the NBT tab. You can set the sequence in which WINS servers and broadcast messages are used from the NBT tab.
If the NetBIOS name is not found, NetBIOS next searches your LM host table on the workstation, if you have enabled it.
Finally, NetBIOS searches the DNS servers you defined on the DNS tab in the Configuration Utility, if you have enabled NetBIOS use of DNS on the NBT tab. In this case, the NetBIOS name must be the same as the TCP/IP host name for NetBIOS to find a match.
The LAN Manager Hosts (LM Hosts) file is similar to the TCP/IP host table; both are files on your workstation that map IP addresses to names. In the case of the LM Hosts file, the name mapped to an IP address is a NetBIOS name.
To build the LM Hosts file, use the LM Host Table tab in the Configuration Utility. As with the TCP/IP host table, only include key NetBIOS name mappings in the LM Hosts file. If you are not using WINS servers, include all NetBIOS names that are not on your local network segment in the LM Hosts file.
If you make any typing mistakes when creating the LM Hosts file, it can prevent you from using NetBIOS communications with the target machine. Also, you must ensure that this file correctly reflects any changes made to the network that involve the machines for which you have entries.
A WINS name server is similar to a DNS server, except that WINS servers return the IP address of a network resource based on the resource's NetBIOS name. When a workstation or other network machine needs to use TCP/IP to deliver NetBIOS packets, it can ask a WINS server for the IP address that belongs to the NetBIOS name of the target machine.
WINS servers build their IP address-to-NetBIOS name mappings automatically from these sources:
Because WINS servers can gather and maintain these mappings automatically, they require little maintenance while being reliable. Thus, they are a good choice for name resolution when using NetBIOS over TCP/IP.
Normally, there should be a WINS server on every segment of the network for WINS to work well. However, instead of having a WINS server on each segment, you can define your workstation as a WINS proxy. If your workstation acts as a WINS proxy, it redirects NetBIOS name queries to a WINS server, and stores the responses in its local NBT cache. Your workstation can then respond to subsequent requests for the NetBIOS name.
Ask your network administrator for the address of your WINS server, if you have one. Your network administrator can also help you determine if your workstation should act as a WINS proxy server.
HTML file generated May 15, 1996.